Thin film composites of polyethylene, a copolymer of ethylene propylene and polyvinyl alcohol have found extensive use in the food packaging industries for meats, vegetables and fruits. The polyvinyl alcohol of these composite films imparts the necessary barrier properties to the composite. The polyethylene imparts the necessary physical properties to the film composite to enable one to have an integral film system. The ethylene/propylene copolymer acts as a binding agent between the ethylene and the polyvinyl alcohol.
The present invention teaches the use of a thin film of a polyalcohol homopolymer for use in the food packaging industry. The use of the polyalcohol homopolymer eliminates the need for the use of film composites because the polyalcohol homopolymer besides exhibiting excellent thermal stability and barrier properties also possesses physical properties which permit the formation of polymeric thin film having sufficient physical integrity.
Polyalcohol like polyvinyl alcohol, ##STR3## are well known useful materials prepared via free radical polymerization of vinyl acetate followed by hydrolysis to polyvinyl alcohol. Such polyalcohols always contain unreacted acetate residues. Also, since the alcohol group is attached directly to the backbone such polymers do not particularly have high thermal stabilizers.
Direct polymerization of alcohol containing monomers, although desirable, is synthetically difficult to achieve. One reason for this situation is that alcoholic functionalities poison organometallic catalysts, like Ziegler-Natta (Al, Ti) catalysts.
Copolymers of alpha-olefins (e.g., ethylene and propylene) with special alcohol monomers, e.g., undecylenyl alcohol, have been reported by Clark [U.S. Pat. No. 3,492,277 (1979)] be pretreating the alcohol with organoaluminum compounds. However, this patent does not teach or suggest polyalcohol homopolymers.